Treatment of Bleeding Episodes With Efanesoctocog Alfa in Previously Treated Patients With Severe Hemophilia A in the Phase 3 XTEND-1 Study.

Despite therapeutic advances, people with hemophilia experience bleeds. These may be life-threatening, result in permanent joint damage, chronic pain, difficulties with mobility/daily activities, and impact quality of life. In the XTEND-1 study (NCT04161495), once-weekly efanesoctocog alfa (50 IU/kg) prophylaxis provided highly effective bleed prevention and high-sustained factor levels for most of the week and was well-tolerated. We report post hoc analysis of bleeding episodes and their treatment in previously treated patients (≥ 12 years old). Participants received 50 IU/kg efanesoctocog alfa either as once-weekly prophylaxis (Arm A) or on-demand followed by once-weekly prophylaxis (Arm B) in XTEND-1. Endpoints included treatment of bleeding episodes and response to treatment. During XTEND-1, 422 bleeding episodes were reported among 159 participants; 362 were treated. Most treated bleeding episodes (74%; n = 268) occurred during the Arm B on-demand period, of which 197 (74%) were spontaneous. Seventy-five participants had no bleeding episodes in Arm A; all in Arm B had ≥ 1 bleeding episode while on-demand. Most participants (n = 107, 81%) had zero treated spontaneous bleeding episodes and rates of treated bleeding episodes in Arm A (prophylaxis) were low (median [interquartile range] overall ABR: 0.00 [0.00-1.04]). A single injection was sufficient to resolve 97% (350/362) of treated bleeding episodes, no bleeding episodes required > 3 injections, and responses to 95% of evaluable injections were rated excellent/good. Median total dose was 50.9 IU/kg per bleeding episode. Results of this analysis further demonstrated that once-weekly efanesoctocog alfa provides highly effective bleed protection and treatment of bleeding episodes in participants with severe hemophilia A. Trial Registration: NCT04161495.